Repeater systems can serve a wide frequency band, for example a complete 3GPP band. A frequency band typically contains multiple carriers carrying information according to different communication technologies and standards such as GSM, UMTS, LTE, or the like.
A repeater system can be used on a train to provide network coverage within the train. High-speed train applications can present extremely challenging RF environments. The complexities of different terrain combined with rapidly changing outdoor signal levels of the various networks can make it difficult for operators to provide the coverage and service their customers demand while travelling from city to city or to another country. To improve the reliability of wireless signals on trains, repeater systems in the shape of distributed antenna systems (DAS) can be cost-effective. A DAS may for example be installed within a train and serve to amplify a signal to compensate an attenuation caused by the train (due to, for example, metalized windows on high-speed trains reducing signal penetration into the train carriages, which may result in spotty coverage and dropped calls).
The signal strength available from macro-cells of base stations outside a train can vary as the train moves. In some areas with good network coverage, the signal inside the train may be strongly overlaid by the base station's original source signal. A mobile station within a train carriage may at the same time receive signals from a base station outside the train on a direct path and on an indirect path via the DAS installed on the train. This multipath propagation can cause dropped connections or can reduce data throughput in case the delay between the signals received via the different paths exceeds some limit.
For example, in an LTE network the delay spread can be limited by the time of the cyclic prefix (CP). If the delay between different signal paths is larger than the CP used, there is a risk that calls are being dropped or that the data throughput is reduced.
A solution to decrease the risk for dropped connections is to increase the CP. This however comes with the inherent drawback of a reduced data throughput.